This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        BSR buffer status report        DL downlink (network towards UE)        eNB EUTRAN Node B (also eNodeB)        EUTRAN evolved UTRAN (also known as LTE or LTE-A)        LTE long term evolution        MME mobility management entity        PDCCH physical downlink control channel        PUCCH physical uplink control channel        PUSCH physical uplink shared channel        RACH random access channel        RF radio frequency        RRC radio resource control        SR scheduling request        UE user equipment        UL uplink (UE towards network)        UTRAN universal terrestrial radio access network        
The examples below are in the context of the LTE system. In the LTE cellular radio system the base station (termed an eNodeB or eNB in LTE) signals on the physical downlink control channel PDCCH the time-frequency resources (physical resource blocks) that lie on the physical downlink shared channel PDSCH and the physical uplink shared channel PUSCH and which are allocated to a mobile terminal (UE). This scheduling protocol allows advanced multi-antenna techniques like precoded transmission and multiple-input/multiple-output operation for the downlink shared data channel. For the case in which a UE has UL data to send, it will send a scheduling request SR to the eNB in order to obtain an UL grant for a PUSCH resource allocation.
There are two different ways in LTE by which a UE can send a SR. If the UE is not in a RRC connected state with the eNB it will use a random access procedure in order to acquire timing synchronization and a temporary identifier for use in the cell as well as the PUSCH allocation it seeks. If the UE is in a RRC connected state with the eNB it can use either random access procedure or periodic SR resources. If periodic SR resources are configured, UE will use one or more of the periodic SR resources on the PUCCH which are dedicated for that particular UE. For any given UE each of these dedicated SR resources may be considered a SR opportunity for that same UE. The transition from blocks 112 to 114 at FIG. 1 below gives an exception by which a UE in the RRC connected state is allowed to use the random access procedure, but only under specific conditions detailed there. If the UE in a connected mode also does not have PUCCH resources then the UE can also use the random access procedure according to the direct transition from block 104 to 114.
The interval of the UE's SR opportunities on the PUCCH is semi-statically fixed between 1 and 80 ms (milliseconds). FIG. 1A illustrates the concept; the UE is configured with a SR cycle which gives the interval between SR opportunities. Shorter intervals and thus more frequent opportunities are configured for UEs with delay critical services, while longer intervals were originally specified in order to allow conserving the PUCCH resources when the network is keeping a large number of UEs with relatively low activity levels in the RRC connected state. There has been some discussions that LTE (or LTE-Advanced which is to be implemented as LTE Release 10) allow even longer SR intervals than is presently specified to more efficiently handle smartphone background traffic. Longer intervals between SR opportunities translate to longer delays when the UE needs to obtaining PUSCH resources for delay critical signaling or data.
Consider a specific example of a UE configured with an 80 ms SR interval. If we assume its signaling need arises immediately after a SR opportunity expires, that UE will first have to wait 80 ms for the first SR opportunity and another 80 ms for each retransmission of its SR if the UE does not receive PUSCH resources because eNB fails to receive the UE's PUCCH transmission or does not have resources to allocate for the UE. In LTE the maximum number of SR transmissions (given by the RRC parameter dsr-TransMax) can be set no lower than four, which means that in the worst case the UE will delay 320 ms, plus a configurable time for waiting the PUSCH grant after the last SR attempt, before it will abandon this attempt to obtain a PUSCH and begin a new attempt. This is a very large latency, particularly for a UE in the RRC connected state. As a point of comparison, LTE requires a maximum of 100 ms latency for a UE not in the RRC connected mode to transition from idle (not RRC connected) to active (RRC connected) states, and 50 ms latency for a UE in the RRC connected mode to transition from dormant to active. Extending the SR interval further would result in the above worst case delay extending latency for transmitting a packet even further.